Gliomas account for 81% of all malignant brain and CNS tumors. Glioblastoma (glioblastoma multiforme (GBM); World Health Organization (WHO) grade IV astrocytoma), in particular, accounts for 60% to 70% of malignant gliomas and remains the most aggressive subtype of glioma. It occurs mostly in adults (median age at diagnosis: 64 years) and its incidence is estimated to be 3.05/100,000 in the United States. With 1- and 5-year overall survival of 29% and 3%, respectively, the prognosis of glioblastoma remains particularly poor (Central Brain Tumor Registry of the United States (2005) (CBTRUS; http://www.cbtrus.org)).
Although some progress has been made in the treatment of glioblastoma, this disease presents a highly unmet medical need with limited treatment options. In particular, bevacizumab (Avastin®), a monoclonal antibody targeted against the pro-angiogenic vascular endothelial growth factor (VEGF), holds significant therapeutic potential.